Expression of the Pho regulon negatively regulates biofilm formation by Pseudomonas aureofaciens PA147‐2

We report the isolation of insertional mutations to the pstC and pstA genes of the phosphate‐specific transport ( pst ) operon that results in loss of biofilm formation by Pseudomonas aureofaciens PA147‐2. Consistent with the known roles of the Pst system in Escherichia coli and Pseudomonas aeruginosa , both P. aureofaciens pst mutants were demonstrated to have defects in inorganic phosphate (P i ) transport and repression of Pho regulon expression. Subsequently, biofilm formation by the wild type was shown to require a threshold concentration of extracellular P i . The two‐component regulatory pair PhoR/PhoB is responsible for upregulation of Pho regulon expression in response to P i ‐limiting environments. By generating phoR mutants that were unable to express the Pho regulon, we were able to restore biofilm formation by P. aureofaciens in P i ‐limiting conditions. This result suggests that gene(s) within the Pho regulon act to regulate biofilm formation negatively in low‐P i environments, and that phoR mutations uncouple PA147‐2 from such regulatory constraints. Furthermore, the inability of pst mutants to repress Pho regulon expression accounts for their inability to form biofilms in non‐limiting P i environments. Preliminary evidence suggests that the Pst system is also required for antifungal activity by PA147‐2. During phenotypic analysis of pst mutants, we also uncovered novelties in relation to P i assimilation and Pho regulon control in P. aureofaciens .